Adding simple gauges -- help needed

Hello everyone and thank you for taking the time to read my post.
I am able to use VCM scanner properly but I want to add a few simple gauges that aren't available.

For example I would like to see a battery voltage gauge, an instant MPG gauge and a average trip MPG gauge.

For the battery gauge, I cloned an existing gauge and clicked on parameter and then added a specific parameter>systems>battery & charging> battery voltage.
Now while the gauge is properly displayed, when I try to review a log that I have made prior to creating the gauge, nothing gets displayed.

It would make sense to add the battery voltage channel before starting to log. However, if I go to add channel>ECM>battery & charging> I cannot locate the battery voltage channel...
I am working on a GM Gen V L86 engine with the 8L90e transmission from a 2015.5 escalade.

I also tried to add the instant MPG gauge using the following formula:
(A-6*[B])*[50020.114]/[6210.72]/[50151.248.avg(700)]/[50070.56]

A = 400 for V8
B= 10 for regular gas (although I use premium, however I am not sure what the number is for premium)

It doesn't seem to work...
under the formula, ID 10 fuel pressure sae and ID 6210 (injector flow rate lb/h) are highlighted.

I would appreciate any help to get these gauges working.
Many thanks!